If biodad is not communicating out of spite, or because he's trying to hide something from you then giving your son a cell phone won't help. Biodad can just take it away from him. That's something that needs to be handled through the courts, and the responsibility of the phone or calling shouldn't be put on the 5yo

If biodad isn't communicating because he's flaky, but otherwise things are okay when your son visits, then there's really no reason he would need a cell phone.

At school, on the bus, 5 is way too young. I guess I think 5 is too young in general to handle a cell phone wisely on his own.

This. And while my 5 1/2 year old loves to play on my phone, there's no way I'd give her one to take care of on her own. She would lose it the first day. And to be honest, there's no reason to worry that she's not safe while she's at her dad's house despite lack of communication. I don't call to check on her because she's where she should be and she's not left to her own devices to get herself from Point A to Point B. That's just too much responsibility to place on her to ask that she call me while she's with daddy. I might ask my 13 year old or MAYBE my 8 year old but even then.....probably not.

What does your husband say? He might have a better feel than any of us for if it is really necessary.

I personally do not call my kiddos when they are spending time with someone else but they can always call me. Are you fine with dad calling him and talking with him at your house? Are you fine with dad checking in on him throughout the week? Cause it really has to go both ways.

Another thought, would his dad like to be able to contact him when he is at your house without going thru you? If so he could have one for when he is at either house. Maybe dad would even split the bill.

Would dad be fine with putting in a landline so ds could call you if he wanted while he was there? Or maybe dad would be willing to let him use his phone and could tell him so.

And I would make sure my kiddos didn't feel like they have to call me for any reason.

My oldest kiddos are almost 15 and 13 and they just take our cheapo phone with them when they go somewhere, I don't see the need for them having their own.

Edited to add:
I agree with the person that said you don't want to make your son feel their is reason to be scared of being at dad's. You need to help him feel safe. Very good point! I know my kiddos definitely can tell how I feel about things and respond accordingly.

5 is WAY too young. He may also not be allowed to even have it in his backpack at school so I would check on that.

IMO kids need cell phones once they start going out ALONE without a parent OR someone you know being in charge. For example my boys are 9 and 10 (almost 10 and 11) and we've dropped them off at track a couple times and done running around until they are done. Next spring if I find I am leaving them at the track club on their own more often I will be getting them a phone. They've also been to the park once alone for a little while (it isn't near our house otherwise I would let them go more often at their ages) they could have used a phone (they were only "alone" for about 20 minutes) if we start letting them go there alone more often they will need a phone.

I gave my son his first cell phone when he started to attend school. He knows he can use it only for calls and message sending, I also told him I spy on him via parental control lol ( this one https://www.mspy.com ). I suppose it's just another safety measure, why not.

I have no experience with your situation, nor do my kids have a cell phone (4 & 8 - though I have been asked).

I voted yes for just bioDads. Not a smartphone and a plan with limited allowed numbers to call. But I would be ready for it to be lost/broken/left at bioDads. Keeping it charged also an issue but if just using for a weekend away, you charging it once would probably work. I wouldn't expect him always to answer either - and that doesn't mean he is not okay.

I think a better solution would be to try to setup a practice that he calls you to say goodnight / good morning from his cell phone or bioDads phone.

Personally I would have said no cell phone, and work on communication with bio dad. You may not be together but you will be co parenting for many years. It would be best to model a functional relationship for DS, and it would have obvious gains for the bio mom and bio dad as well.

Also, I get being concerned about your child when they aren't around, but unless bio dad has a history of putting DS in harm's way, the lack of trust/desire to control the other parents time is unfair. I am guessing the bio mom would not be happy if bio dad did not trust her to parent and keep the child safe, and he called frequently to see where the child was and make sure he is ok.